Vapor electric device



April 1955 G. LEWIN ETAL VAPOR ELECTRIC DEVICE Filed June 29, 1951 INVENTORS GEM/Hep LEW/Al E: H- GOLDMfl/V. BY 5R7 ATTORNEY United States Patent VAPOR ELECTRIC DEVICE Gerhard Lewin, Maplewood, and Ernest A. Goldman, Bloomfield, N. J., assiguors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 29, 1951, Serial No, 234,422

Claims. (Cl. 313170) The invention relates to vapor-electric devices and as a particular example to such as are generally known as ignitrons.

Attempts have heretofore been made to provide a porous or sponge cathode for electric discharge devices wherein mercurcy is repetitiously absorbed by the sponge, and the present invention contemplates improvement thereover.

Sponge cathodes of this type usually comprise a porous iron body with an insert in its upper face to constitute the arc-striking area, the insert being of a different sponge material of which molybdenum is an example. The main difliculty experienced in the preparation of these cathodes is to render and retain the metal, particularly the metal of the isert, wettable by the mercury. In the past it has been found that an elaborate cleaning process was required, and after the cleaning was accomplished to then avoid further contact of the sponge cathode with air, as that would again, in a few seconds, render the metal of the sponge unwettable by mercury. While the cleaning can be accomplished in a glass enclosure, there is then difiiculty in transferring the sponge cathode to its place of use in an evacuated metal container. Cleaning directly in the metal container is not practical, because other tube parts tend to give off gases which poison the sponge. The ignitor, in particular, reacts with the hydrogen used in the cleaning operation. Gaseous compounds are formed which react with the metal of the sponge and render the sponge, especially the insert thereof, non-wettable by the mercury.

In the broad aspect of the invention, more certain wetting by the mercury or other reconstructive cathode material on the outer and inner surfaces of the sponge body, is a primary objective.

A further object of the invention is to provide a cathode body which may be readily prepared and transferred to place without exposure to poisoning.

Another object of the invention is to provide a cathode body of a character not aifected adversely by stand by periods, either before or after installation in place of use.

Other objects of the invention will appear to those skilled in the art to which the invention appertains as the description proceeds, both by direct reference thereto and by implication from the context.

Referring to the acccompanying drawing, in which like numerals of reference indicate the same parts in both views thereof:

Fig. 1 is a central longitudinal sectional view of an ignitron of arbitrarily selected construction showing our invention embodied therein; and

Fig. 2 is a cross-section on line 11-11 of Fig. 1.

In the specific embodiment of the invention and associated ignitron construction illustrated in the drawing, but without limiting to the details thereof, a cylindrical casing of steel or other sturdy material is shown having a bottom 12 integral therewith and a top header 13 sealed at the upper rim of said casing to provide a closed envelope adapted to be evacuated.

The particular header shown, provides appropriate leadin seals 14, 15 for electrode leads 16, 17 respectively for an anode 18 and ignitor 19 within the casing and supported from said header by said leads. The lead-in seals each include a glass or other insulating sleeve 20 by which the leads are kept electrically distinct from each other and from the casing. The anode 18 is located toward the top of the casing, well above the bottom wall 12, wherewhereas the ignitor 19 is located below the anode, preferably centrally of the casing, and is directed toward and terminates at its bottom in the vicinity of said bottom wall. Said ignitor is shown as relatively slender and tapers downwardly, with its bottom end quite small. Said ignitor may be composed of materials as used for ignitors of the prior art, or may be of such other material or materials adapting it more especially to the present invention.

A sponge cathode, designated generally by numeral 21, is provided in said container and is of pan-cake shape, and situated upon the bottom wall 12 of the ignitron, preferably fitting the container at its periphery and frictionally or otherwise held permanently in fixed position. The aforementioned lower small end of the ignitor 19 rests upon the upper surface of the sponge cathode 21 in constant contact therewith, and as one means for main taining such contact without detriment to the lead-in seal 15, the lead-in 17 for the ignitor, between the seal and the ignitor, is shown with a transversely extending section 22 which, with the rest of said lead-in, possesses adequate resiliency, supplemented by the weight of the ignitor, to accomplish the purpose. The ignitor projects, from its contact on the sponge cathode, at right angles thereto and in a direction longitudinally of the casing. Mercury or other reconstructing liquid cathode material is applied to the sponge cathode 21 to the extent that said sponge will absorb the mercury or the like without any excess remaining on the surface. The sponge cathode 21, with the absorbed mercury, constitutes the cathode of the ignitron.

In the specific showing of the drawing. the sponge cathode 21 is constructed essentially of two different materials, of which one is used to take advantage of its relatively large interstices between granules for providing generous reservoir capacity, and also to take advantage of its characteristic of afiinity for and absorption of the mercury coming in contact therewith. Selection of the other essential material to constitute the sponge cathode is for purposes of providing an arc-striking surface generously supplied by capillarity through said material with mercury or the like, and to take advantage of resistance to erosion of this other sponge material during operation. More specifically, the present invention proposes for cathode 21 use of a body portion 23 essentially of sintered iron or other material having high absorptive afiinity for the reconstructing cathode fiuid, such as the mercury above mentioned, and an arc-striking portion 24 essentially a sintered metal, of which molybdenum, tungsten and tantalum are appropriate examples.

In the specific disclosure arbitrarily selected for illus tration in the drawing, the body portion 23 of the sponge cathode is shown relatively fiat or thin, of pan-cake shape to fit within the bottom portion of the container flatwise on the bottom wall thereof and frictionally or otherwise held fixed in that position. The arc-striking portion 24 is shown as a smaller disc than said body portion and embedded therein concentric thereto and according to the like to said arc-striking portion and by capillary action through the arc-striking portion the mercury is ever present at the arc-striking surface.

The body portion 23 of compressed sintered granules essentially iron, is employed in conjunction with the centrally disposed arc-striking portion 24 of compressed sintered granules of molybdenum or other material, such as tungsten or tantalum, to take advantage of the inherent characteristic of the iron sponge of more active absorption of mercury coming in contact therewith than would occur with a similarly compressed sintered body of molybdenum or other metals of the group having the absorptive characteristic.

in manufacture of the sponge cathode, the powdered material is compacted and sintered to form the cake in its final size and configuration for use with or without machining, as desired. As a feature of the present invention, the sintered cake is then thinly coated, as by evaporation process, with a coating 25, of which copper, gold and platinum are examples. Said coating is preferably very thin, say approximately 0.5 micron. Next the sintered and coated cake is cleaned thoroughly. The cleaning is effected at elevated temperature, and preferably at red heat, by enclosing the cake in a glass container which is evacuated, following which hydrogen is admitted to the container and the cake therein, the hydrogen later being pumped out and the cake again subjected to vacuum. During this second period of evacuation, and preferably after cooling, mercury is admitted to the cake and is absorbed by the cake in a very considerable quantity. Admission of mercury is continued until no more is absorbed.

While the copper or other coating is of thin enough character to admit the mercury into the sponge material of the cake, it has been found to prevent subsequent penetration of oxygen from the air into the sponge metal-mercury interface. It is apparently such oxygen which in prior practice has been the cause of drying the surface and rendering a sponge cathode non-wettable by mercury.

The theory is advanced that probably the mercury and copper form an amalgam which seals the interface to oxygen but is readily wettable by the mercury. Irrespective of theory, it has been found in practice that a sponge cathode or cake thus made can be left exposed to the air for a long period and thereafter incorporated in an ignitron and is readily wettable by the mercury therein and functions perfectly as a cathode. Sponge cakes not provided with the copper or other metal coating become unwettable by mercury a few seconds after exposure to air, and thus the present invention solves the prior art difficulty of transfer of the sponge cake from the cleaning vessel to the ignitron container and evacuation of the ignitron container before deleterious drying of the cake takes place.

We claim:

1. A sponge cathode comprising a cake of spongy material, a copper coating upon the spongy material, and a liquid material absorbed in the spongy material.

2. A sponge cathode comprising a cake of spongy material comprising at least one of the group of molybdenum, tungsten and tantalum, a coating of copper upon the spongy material, and a liquid material absorbed in the spongy material.

3. An ignitron having a sponge cathode copper coating on said sponge cathode.

4. A sponge cathode comprising a body portion of a first spongy material, an arc-striking portion of a second spongy material, said arc-striking portion being imbedded in said body portion, a metallic coating upon at least one surface of said body portion and said arc-striking portion, and a liquid material absorbed in said body portion and said arc-striking portion.

5. A sponge cathode comprising a body portion of a first spongy material, an arc-striking portion of a second spongy material, said arc-striking portion being imbedded in said body portion, a metallic coating of substantially 0.5 micron thickness upon at least one surface of said body portion and said arc-striking portion, and a liquid material absorbed in said body portion and said arc-striking portion.

therein, and a References Cited in the file of this patent UNITED STATES PATENTS 1,591,432 Noble July 6, 1926 2,118,887 Jurriaanse May 31, 1938 2,128,861 Tonks Aug. 30, 1938 2,128,862 Tonks Aug. 30, 1938 2,183,102 Jurriaanse Dec. 12, 1939 2,218,386 Smith Oct. 15, 1940 2,432,513 Depew Dec. 16, 1947 2,468,037 Clark Apr. 26, 1949 2,640,171 Lewin et al. May 26, 1953 

1. A SPONGE CATHODE COMPRISING A CAKE OF SPONGY MATERIAL, A COPPER COATING UPON THE SPONGY MATERIAL, AND A LIQUID MATERIAL ABSORBED IN THE SPONGY MATERIAL. 